This invention relates to a light control apparatus to control the quantity of incident light utilizing the changes in optical transmissivity of an electrochromic element.
In recent years, the importance of the earth's resource conservation efforts has been receiving great attention and energy saving activity as part of such efforts is becoming important. As one of the specific ways to save energy, it is considered important to try to make the most of daylight in planning on construction of houses and offices. There is a report that productivity at a factory is enhanced by lighting the factory by funneling daylight into it. Also, it is considered very valuable to develop a method of controlling the daylight utilization for interior illumination. One simple daylight controlling system is a window-shade. One recently developed system is an application of an electrochromic element in the form of a dimming glass which has a construction of transparent electroconductive layers, an electrochromic layer and an electrolyte being contained between dimming glass substrates. When a DC voltage of 1.5 to 3 volts is applied across the transparent electroconductive layers, a reducing process takes place in the electrochromic layer with resultant coloring of the dimming glass. The optical transmissivity of the dimming glass is changed according to the application period of the voltage. In addition, a reversed reaction is caused when the polarity of the applied voltage is reversed, with resultant color vanishing of the dimming glass.
This is explained in FIG. 4, which primarily shows a cross-sectional view of an electrochromic element. An electrochromic element comprises at least two of a dimming glass substrate 11, two of a transparent electroconductive layer 12 for applying a voltage between the two dimming glass substrates, an electrochromic layer 13 for a reducing reaction and an electrolyte 14 as a source of ions. Besides, FIG. 4 shows a sealing material 15, bus bars 16 serving as the terminals for voltage application, an intermediate layer 17, a counter electrode 18 and a DC power supply 19.
When a DC voltage from the DC power supply 19 is applied across the transparent electroconductive layers 12, a reducing reaction takes place in the electrochromic layer causing it to take on a color. On the other hand, an oxidation reaction takes place at the surface of the counter electrode 18 and proceeds until it reaches a point where a balance is taken between the reducing reaction and the oxidation reaction according to the law of conservation of charge, with a resultant completion of coloring of the electrochromic element. Thus, it is possible to control light with the optical transmissivity of the electrochromic element being changed.
Moreover, even after elimination of the applied DC voltage, the status of coloring of the electrochromic element is sustained due to a memory effect. When the polarity of the applied voltage is reversed, the color of the electrochromic element vanishes due to a reversed reaction taking place within the element. The optical transmissivity (depth of color) of the electrochromic element can be controlled by the quantity of electric charge passing through the element.
When the aforementioned window-shade is used in controlling light, a special fixture for the window-shade has to be installed, resulting in a rather complicated appearance around the window. Besides, a window-shade provides means of adjusting incident daylight only by either horizontal slatting or vertical slatting. In the case of the foregoing dimming glass of a relatively recent development as applied to a light control system, the dimming glass just replaces the whole ordinary glass pane covering a window opening, providing the whole window area with a uniform light controlling capability, not providing a capability of controlling light with its intensity varied from place to place. Therefore, when strong daylight is transmitted through the dimming glass causing the light reflection on a desk near the window to be too strong, the optical transmissivity of the electrochromic element as used in the dimming glass has to be lowered uniformly over all of the glass area, not allowing a regional control of the light with resultant inefficiency in utilizing the daylight. Besides, the daylight taken in is dispersed by the dimming glass resulting in an elimination of the directional qualities, by which the daylight interior illumination is characterized.